Grid metal alloy



States Patett Patented Nov. 16, 1954 GRID METAL ALLOY Walter PeterCarroll, Cicero, 11].; Alice Mary Carroll,

executrix of said Walter Peter Carroll, deceased, assignor to NationalLead Company, a corporation .of New Jersey No Drawing. Application July14, 1951, Serial No. 236,863

2 Claims. (Cl. 75-166) This invention relates to lead alloys; Moreparticularly, it relates to an improved grid metal alloy for storagebatteries of the lead-acid type.

It is generally recognized that the life of storage batteries is oftenlimited by the corrosion of the positive grid metal structure. Leadalloys with from seven to ten percent or more antimony have been foundby past experience to possess good corrosion resistance in batteryacids. Small amounts of tin have been universally added to obtain bettercastibility. However, it has also been generally known that the antimonycontent results in self discharge of the battery when standing duringperiods of non-use and also sulfation of the negative plate; andattempts have been made to eliminate the antimony or to reduce theantimony content. In such cases, the corrosion resistance of thepositive grid structure suifers as does the stiffness of the grids.Moreover, castibility of the grid alloy is afiected due to loweredfluidity in the molten state and good castings of a fine thin gridstructure are difficult to obtain. This has resulted in uneconomicalreturn of pure castings to the melting pot.

In attempts to add hardening agents, the corrosion resistance has notgenerally been improved. The addition of a tenth percent alkaline earthmetal to pure lead has resulted in an improvement in self discharge butcastibility and corrosion resistance under ordinary conditions arelacking. Even in the case of silver additions, for instance, withantimony lowered to about four percent, the self dischargecharacteristics of the battery are not acceptable.

The principal object of this invention is to provide a lead alloysuitable for the manufacture of storage battery grids which will becharacterized by improved corrosion resistance, good castibility andresult in lowered self discharge, on standing idle, of batteries inwhich it is employed. This and other objects of the invention will beapparent from the following more complete description thereof.

In its broadest aspects, this invention contemplates the provision of agrid metal alloy containing:

Antimony from 0.2 to 0.6% Tin from 0.2 to 2.5% Arsenic from 0.05 to0.75% Silver from 0.05 to 0.25 Copper from 0.02 to 0.10% Tellurium from0.05 to 0.25% Lead, balance A preferred alloy contains:

0.75% tin 0.45% antimony 0.35% arsenic 0.15% silver 0.08% copper 0.06%tellurium Balance, lead It will be noted that the anitmony content ofthe alloy of this invention is substantially lower than the 9% antimonygrid metal heretofore generally employed. According to the presentinvention, antimony may be incorporated in the grid metal alloy inamounts up to the maximum of solid solution of antimony in lead at thetemperature of use; for the purpose here intended, this will ordinarilybe about 0.6%. The tin content has been found, in combination with theother alloying elements, to promote castibility of the alloy in themolten state. The arsenic and copper are present in amounts generallyabove those heretofore considered maxims for grid metal alloys. Theamounts of these metals, together with the silver and tellurium, arecritical in obtaining corrosion resistance of the alloy while in servicein the battery without having a deleterious efiect on the self-dischargecharacteristics.

The alloy of this invention may be manufactured according to methodsknown in the art and to a molten bath of lead may be added the variousalloying elements in proper proportions to form the final alloy.

In order to illustrate the practice of this invention, a grid metalalloy containing 0.75% tin, 0.45% antimony, 0.35% arsenic, 0.15% silver,0.08% copper, and 0.06% tellurium was formed by adding these alloyingelements to molten lead. Storage battery grids of the automotivestarting, lighting and ignition type, having a thickness of about 0.078inch were cast in the usual manner from this alloy. Experimentalbatteries were manufactured, employing the so-formed grids which werepasted with active materials in the positive plates comprising leadoxide containing about 30% finely divided metallic lead and in thenegative plates with similar oxide containing about 0.5% of conventionalexpander materials. The batteries contained 15 plates, were of Group Isize, of nominal ampere hour capacity. Similar test batteries weremanufactured, identical with those described above, except that thegrids were cast, in one case, from conventional 9% antimony-lead gridmetal alloy and, in the other case, from commercial pure lead.

The batteries described above were subjected to the standard SAEovercharge life test for which the standard calls for a minimum life forthe battery of five weeks. In this test, the batteries were brought tofull charge and then discharged at 300 amperes. The number of minutesfor discharge was noted. The batteries were then given 990 ampere hoursof continuous charge at a 9 ampere rate withbatteries in a water baththermostatically controlled at a temperature of 100:5 F. This was doneduring a period of five days from each Monday to Friday and then aperiod of standing on open circuit for two days over the weekend ensued.The batteries were then given a 300 ampere discharge, to an end voltageof 1.20 volts per cell, or to a minimum discharge time of 30 seconds,whichever occurred first. This cycle was then repeated weekly until thebattery failed to meet either of the requirements specified, at whichtime the battery was taken out of test. Comparative tests were also madeon self discharge characteristics by noting the comparative drop inspecific gravity of the electrolyte in the batteries after standing idlefor twenty-eight days. The comparative figures are expressed in terms ofthe greatest loss, the 9% antimony grid taken as 100.

b iIhe results of these tests are summarized in the table e ow:

Table overcharged Comparative Grid Metal SAE Life, Self Dls- Castlbllltywks. charge 18-20 63 good. 4-6 40 poor. 8-10 100 Excellent.

COMPOSITION OF ALLOYS TESTED Anti- Arse- Tellur- Grid Metal mony Tm meCopper Silver mm 1. Alloy of this invention 0. 45 0. 75 0. 35 0. 08 0.15 0. 06 2. Pure Lead 0.003 None 0.001 0. 001 0.001 None 3. 9%antimonlal lead 9. 24 0.3

It will be noted from the results above that the conventional 9%antimony-lead alloy shows excellent castibility, poor self dischargecharacteristics, and only fair life due to corrosion of the grids. Thebattery containing pure lead grids showed poor castibility, poor lifeand good self discharge characteristics. The grid metal alloy of thisinvention showed good castibility, substantially improved life,indicating superior corrosion resistance of the grids, and better selfdischarge characteristics in a battery than the 9% antimony lead. Thealloy of this invention therefore provides a long desired combination ofproperties which are not found either in the pure lead or inconventional grid metal.

While this invention has been described and illustrated by theembodiments shown, it is not intended to be strictly limited thereto andother modifications and variations may lieemployed within the scope ofthe following claims.

0 arm:

1. A grid metal alloy consisting essentially of from 0.2% to 0.6%antimony, from 0.25% to 2.5% tin, from 0.05% to 0.75% arsenic, from0.02% to 0.10% copper, from 0.05% to 0.25% silver, and from 0.05% to0.25% tellurium and the balance lead.

2. A grid metal alloy substantially of the following composition:Antimony 0.45%, tin 0.75%, arsenic 0.35%, copper 0.08%, silver 0.15%,tellurium 0.06%, balance lead.

4 References Cited in the file of this patent UNITED STATES PATENTSNumber Name Date 480,266 Knowles Aug. 4, 1892 2,107,223 Swartz Feb. 1,1938 2,148,741 Gonser Feb. 28, 1941 2,333,072 Lighton Oct. 26, 1943FOREIGN PATENTS Number Country Date 326,818 Great Britain Mar. 18, 1930473,781 Great Britain Oct. 20, 1937 OTHER REFERENCES Fink et al.,Treatise in Trans. of the Electrochem. Soc., vol. 79, 1941, pages269-305 (particularly pages 269, 272, 273, 293, 303-305).

1. A GRID METAL ALLOY CONSISTING ESSENTIALLY OF FROM 0.2% TO 0.6%ANTIMONY, FROM 0.2K% TO 2.5% TIN, FROM 0.05% TO 0.75% ARSENIC, FROM0.02% TO 0.10% COPPER, FROM 0.05% TO 0.25% SILVER, AND FROM 0.05* TO0.25% TELLURIUM AND THE BALANCE LEAD.